The focus of the proposed research is on cortical development in the absence of input from specific sensory input from the thalamus. I will utilize a novel mouse model (Gbx-2x Ror-alpha-cre) in which thalamic input mainly from the MGN, which relays auditory information to the cortex, will be eliminated, or severely reduced, and I will examine the subsequent development of inter- and intra-cortical connections, and aspects of thalamic development. Anatomical tracing techniques will be combined with molecular techniques in order to determine the influence of thalamic input on the formation of connections and patterns of gene expression throughout development. Specifically, I will examine the development of reciprocal projections from the auditory cortex to the MGN, the topography of projections of thalamic afferents, and also the development of intracortical connectivity and molecular identity of the cortex in the absence of input from a specific sensory system. Fluorescent anatomical tracers will be utilized to study temporal and spatial patterns of thalamocortical, corticothalamic and intracortical projections. This anatomical data will be directly related to studies of gene expression (as determined by in-situ hybridization).